The quality of interactions between infants and their mothers is widely held as a primary process affecting infant development. The Mutual Regulation Model (MRM) conceptualizes infants and their mothers as co- regulating their social interactions by responding to each other's communicative displays of their needs and intentions on a moment-to-moment basis. A major tenet of the MRM is that stressing either the mother or infant will disrupt their regulatory capacity leading to interactive disorganization. Oddly, while experimental manipulations have been developed to examine infant capacities for regulation of a stressor (e.g., arm restraint, the still-face), few studies have examined mothers' capacity for regulation when she is experimentally stressed and how such a disruption dysregulates her infant. To help fill this gap in the research, the goal of this project is to experimentally manipulate maternal exposure to stress for first-time mothers and their infants and to study the stressors' cascading effects on the organization of the dyadic-interactive regulatory system in both a typical, full-term and stress-vulnerable, preterm sample of infants and their mothers. Within each group, dyads will be randomly assigned to one of two experimental conditions, an experimental maternal stress or non- stress condition. Following a resting physiological baseline, all dyads begin with a baseline face-to-face play episode (PlayBL) to evaluate pre-stress regulatory communicative behaviors and physiology. Next mothers participate in the maternal stress condition in which they listen to a known parental stressor, infant distress cries, or a non-stress condition in which they listen to << infant positive vocalizations>>. Both groups will then experience the Face-to-Face Still-Face (FFSF) paradigm which consists of a play episode (Play1), followed by the still-face (SF) infant stressor, and a final play episode (Play2). Individual and dyadic stress effects will be evaluated using a unique combination of multiple measures that includes behavior, salivary hormones, cardiac, and electrodermal activity collected from mothers and infants, and self-reported stress recorded from mothers. The proposed project will introduce a reliable paradigm for manipulating maternal stress and will evaluate the immediate and direct effects of stress on dyadic organization. Knowledge gained from this study will help in identifying mothers who are more vulnerable to stress which in the long run has the potential to continually disrupt dyadic interactions and subsequently compromise the infant's capacity for healthy emotion regulation and development.